PCT publication WO85/02907 discloses a method for surface analysis in which the surface to be examined is bombarded by an ion beam and the liberated particles are ionized by non-resonant photoionization by means of a high-intensity laser beam parallel to the surface. The produced ions are analyzed by mass spectroscopy with a time-of-flight mass spectrometer of the type "Reflektron".
Non-resonant (non-selective) ionization by means of high-power lasers makes possible the identification of substances with very high sensitivity, but quantification, i.e., a quantitative analysis, has not heretofore been attainable. The above-cited PCT publication states that a saturation of ionization by non-resonant multi-photon ionization is possible but that is true only to a limited degree as shown by more thorough experiments and the cited publication also clearly suggests the semiquantitative character of the described method.
In practice, exact quantification is not possible with the known non-resonant laser ionization methods because of the complicated ionization processes and the multitude of parameters, some of which depend on laser intensity. The term "quantification" refers to the possibility, for a given minimum laser intensity, of deriving the concentration of a substance (element) within a given spatial region ("test volume") from the corresponding ion intensity (i.e, an ion signal).